1. Field of the Invention
The present invention relates to an inkjet recording apparatus.
2. Description of the Related Art
Among inkjet recording apparatuses, a continuous ejection type inkjet recording apparatus is a highly stable droplet ejection apparatus having higher reliability and higher maintainability compared with an ondemand type inkjet apparatus used in a printer for home use or office use.
Therefore, the continuous ejection type inkjet recording apparatus can be applied to a manufacturing apparatus for an electronic apparatus for which functional ink application and patterning need to be performed using liquid. High reliability, high maintainability, and high stability are required for the manufacturing apparatus.
The continuous ejection type inkjet recording apparatus pressurizes, using a pump or the like, liquid (ink) stored in an ink tank and continuously ejects the liquid from fine nozzles. The nozzles are vibrated by excitation by a piezoelectric element or the like, fluctuation is applied to the liquid being ejected, and an ink column being ejected is cut to let fine droplets of the ink to fly. At this point, a charging electrode is arranged near a droplet forming position where the ink column is cut and an electric field is applied to the fine droplets of the ink to charge droplets to be formed.
A flying direction of the charged droplets is controlled according to presence or absence and the magnitude (field intensity) of an electric field generated by application of a voltage to a deflecting electrode arranged in a downstream position of the charging electrode (a deflecting process).
The deflecting process is roughly classified into two types, i.e., a multiple deflection type and a binary deflection type. In both types, a charging amount to the liquid (the ink) after ejection is controlled and used for deflection of the liquid. Therefore, discharge control for the droplets does not need to be performed for each of the droplets and the configuration of the apparatus is simplified. Since droplet ejection is continuously performed, nozzle clogging less easily occurs and high reliability can be secured.
However, in most continuous ejection type inkjet recording apparatuses, since an interval between the flying droplets are small, the following droplet combines (merges) with the preceding droplet or disperses (scatters) with Coulomb repulsion to cause an error (distortion) in printing. Therefore, a measure is taken to insert dummy uncharged droplets among charged droplets for printing. As a result, printing speed decreases.
Concerning determination of a droplet interval, it is theoretically known that an ejected liquid column (having a radius “a”) is optimally split into droplets having the same diameter when there is a relation k·a=1/(2)1/2 between the radius “a” and a wave number k of excitation. From this relation and a relation between the ink column to be split and a droplet volume, a relation between a droplet interval L and a droplet diameter d is L=2.36d. Therefore, when the droplet diameter d is determined, the droplet interval L is nearly determined.
In general, it is known that, when another particle flies within a distance 6d behind a flying leading particle (having a diameter d), air resistance (drag) of the following particle decreases to 60 to 80%. Therefore, in the continuous ejection type inkjet recording apparatus, the following droplet catches up and combines with the leading droplet or disperses to cause distortion in printing.
Therefore, in the technique described in JPA61120766 (Patent Literature 1), the deflecting electrode on the ground side is extended in parallel to the deflecting electrode on the positive side in the ink droplet intrusion inlet direction to increase a charged droplet interval.
In the technique described in JPA04292951 (Patent Literature 2), the deflecting electrode on the positive side is obliquely arranged.
In the technique described in JPA2002264339 (Patent Literature 3), the downstream side of the deflecting electrode is formed obliquely along the deflection of the ink droplets.
However, in Patent Literature 1, although the electric field (the electric line of force) tilts with respect to the traveling direction of the ink droplets, since the electric line of force is made incident on the electrode vertically, such an electric field distribution is theoretically impossible. Usually, the continuous ejection type inkjet recording apparatus negatively charges droplets, makes ink incident near the ground electrode, and deflects the droplets in the direction of the positive electrode according to a charging amount. Therefore, in the vicinity of the ground electrode, since the electric line of force is made incident on the electrode vertically, a traveling direction acceleration effect by the electric field is hardly obtained.
In the deflecting electrode structure described in Patent Literature 2, the deflecting electrode surface on the negative side (or the ground side) near the ink droplet incident line is parallel to the ink droplet incident line. Therefore, since there is no electric field component in the traveling direction, an accelerating effect in the traveling direction is hardly obtained.
In the deflecting electrode structure described in Patent Literature 3, the electric field in the ink incident line direction acts as a brake to the contrary. Therefore, an accelerating effect in the traveling direction is hardly obtained.